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Title: Measurement of the Luminous-Region Profile at the PEP-II IP, And Application to e^\pm Bunch-Length Determination

Abstract

The three-dimensional luminosity distribution at the interaction point (IP) of the SLAC B-Factory is measured continuously, using e{sup +}e{sup -} {yields} e{sup +}e{sup -}, {mu}{sup +}{mu}{sup -} events reconstructed online in the BABAR detector. The centroid of the transverse luminosity profile provides a very precise and reliable monitor of medium- and long-term orbit drifts at the IP. The longitudinal centroid is sensitive to variations in the relative RF phase of the colliding beams, both over time and differentially along the bunch train. The measured horizontal r.m.s. width of the distribution is consistent with a sizeable dynamic-{beta} effect; it is also useful as a benchmark of strong-strong beam-beam simulations. The longitudinal luminosity distribution depends on the e{sup {+-}} bunch lengths and vertical IP {beta}-functions, which can be different in the high- and low-energy rings. Using independent estimates of the {beta}functions, we analyze the longitudinal shape of the luminosity distribution in the presence of controlled variations in accelerating RF voltage and/or beam current, to extract measurements of the e{sup +} and e{sup -} bunch lengths.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
876035
Report Number(s):
SLAC-PUB-11682
TRN: US0601020
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Prepared for Particle Accelerator Conference (PAC 05), Knoxville, Tennessee, 16-20 May 2005
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; BEAM CURRENTS; BENCHMARKS; COLLIDING BEAMS; DISTRIBUTION; LUMINOSITY; MONITORS; SHAPE; STANFORD LINEAR ACCELERATOR CENTER; Accelerators,ACCPHY

Citation Formats

Viaud, B.F., /Montreal U., Kozanecki, W., /DSM, DAPNIA, Saclay, Narsky, I.V., /Caltech, O'Grady, C., Perazzo, A., and /SLAC. Measurement of the Luminous-Region Profile at the PEP-II IP, And Application to e^\pm Bunch-Length Determination. United States: N. p., 2006. Web.
Viaud, B.F., /Montreal U., Kozanecki, W., /DSM, DAPNIA, Saclay, Narsky, I.V., /Caltech, O'Grady, C., Perazzo, A., & /SLAC. Measurement of the Luminous-Region Profile at the PEP-II IP, And Application to e^\pm Bunch-Length Determination. United States.
Viaud, B.F., /Montreal U., Kozanecki, W., /DSM, DAPNIA, Saclay, Narsky, I.V., /Caltech, O'Grady, C., Perazzo, A., and /SLAC. Fri . "Measurement of the Luminous-Region Profile at the PEP-II IP, And Application to e^\pm Bunch-Length Determination". United States. doi:. https://www.osti.gov/servlets/purl/876035.
@article{osti_876035,
title = {Measurement of the Luminous-Region Profile at the PEP-II IP, And Application to e^\pm Bunch-Length Determination},
author = {Viaud, B.F. and /Montreal U. and Kozanecki, W. and /DSM, DAPNIA, Saclay and Narsky, I.V. and /Caltech and O'Grady, C. and Perazzo, A. and /SLAC},
abstractNote = {The three-dimensional luminosity distribution at the interaction point (IP) of the SLAC B-Factory is measured continuously, using e{sup +}e{sup -} {yields} e{sup +}e{sup -}, {mu}{sup +}{mu}{sup -} events reconstructed online in the BABAR detector. The centroid of the transverse luminosity profile provides a very precise and reliable monitor of medium- and long-term orbit drifts at the IP. The longitudinal centroid is sensitive to variations in the relative RF phase of the colliding beams, both over time and differentially along the bunch train. The measured horizontal r.m.s. width of the distribution is consistent with a sizeable dynamic-{beta} effect; it is also useful as a benchmark of strong-strong beam-beam simulations. The longitudinal luminosity distribution depends on the e{sup {+-}} bunch lengths and vertical IP {beta}-functions, which can be different in the high- and low-energy rings. Using independent estimates of the {beta}functions, we analyze the longitudinal shape of the luminosity distribution in the presence of controlled variations in accelerating RF voltage and/or beam current, to extract measurements of the e{sup +} and e{sup -} bunch lengths.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2006},
month = {Fri Feb 10 00:00:00 EST 2006}
}

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  • We present a novel method to characterize the e{sup {+-}} phase space at the IP of the SLAC B-factory, that combines single-beam measurements with a detailed mapping of luminous-region observables. Transverse spot sizes are determined in the two rings with synchrotron-light monitors and extrapolated to the IP using measured lattice functions. The specific luminosity, which is proportional to the inverse product of the overlap IP beam sizes, is continuously monitored using radiative/Bhabha events. The spatial variation of the luminosity and of the transverse-boost distribution of the colliding e{sup {+-}}, are measured using e{sup +}e{sup -} {yields} {mu}{sup +}{mu}{sup -} eventsmore » reconstructed in the BABAR detector. The combination of these measurements provide constraints on the emittances, horizontal and vertical spot sizes, angular divergences and {beta} functions of both beams at the IP during physics data-taking. Preliminary results of this combined spot-size analysis are confronted with independent measurements of IP {beta}-functions and overlap IP beam sizes at low beam current.« less
  • We measured the lengths of colliding e{sup +}e{sup -} bunches in the PEP-II B Factory at SLAC using various techniques. First, at several RF voltages and with both single-bunch and multibunch beams, a synchroscan streak camera measured synchrotron emission through a narrow blue filter. With 3.8 MV of RF, the length of a single positron bunch was 12 mm at low current, rising to 13 mm at 1.5 mA and 14.8 mm at 3 mA. The electrons measured 12.2 mm at 16 MV with little current dependence. Both are longer than the expected low-current value of 10 mm (e{sup +})more » and 10.5 mm (e{sup -}), derived from the energy spread and the measured synchrotron tune. We also determined the length for multibunch fills from measurements between 2 and 13 GHz of the bunch spectrum on a BPM button. After correcting for the frequency dependence of cable attenuation, we fitted the measured spectrum to that of a Gaussian bunch. At 3.8 MV, the positron measurement gave 13.2 mm at 1.5 mA/bunch in a full ring, shorter than the 15.6 mm found with the streak camera under these conditions, but we found 11.4 mm for the electrons at 16.7 MV and 1 mA/bunch, in good agreement with the 11 mm from multibunch streak measurements.« less
  • By scanning gated cameras and gated tune monitors across the bunch pattern during normal colliding-bunch operation of PEP-II, the tunes and beam sizes of individual bunches were measured simultaneously in the high and low energy storage rings of PEP-II. The measurements were made with 1561 colliding bunches in PEP-II, arranged in trains of 66 bunches, with each bunch in the train separated by 4.2 ns. The tune and beam size measurements were correlated with the current, luminosity, and specific luminosity of the bunch. The results show a vertical tune shift at the start and end of the mini-trains, a luminositymore » droop along the mini-train, and specific luminosity drop in the first and last bunches of the train, since they experience a different parasitic crossing on either side of the interaction point (IP).« less
  • No abstract prepared.
  • The PEP II B Factory requires a feedback system to damp out longitudinal synchrotron oscillations. A time-domain bunch-by-bunch feedback system has been proposed in which each bunch is treated as an oscillator being driven by disturbances from the other bunches. The phase is detected, filtered, and the feedback correction signal is applied by the kicker. Since we are damping energy oscillations using measurements of phase, the required feedback signal must be proportional to the amplitude of the phase oscillations but phase shifted by 90 degrees. This signal must be calculated for each of the 1658 bunches, in parallel. In themore » original proposal, it was estimated that a farm of approximately 480 digital signal processors (DIPS) would be required to implement the feedback system. However, using the technique of downsampling, this number can be reduced to about 50 DIPS. In what follows, we will briefly explain the basic idea of downsampling and its implementation.« less